Hydraulic circuit for machine tools



Dec. 2, 1941. P. s. JACKSON 2,264,532

HYDRAULIC CIRCUIT FOR MACHINE-TOOLS Filed June 6, 1939 INVENTOR. Mk5:L/MSOWZ BY 5&2 n 8* RNEY twenty feet and less per minute.

Patented Dec. 2, 1941 2,264.53; 7 HYDRAULIC cmcurr Fon MACHINE TOOLSPaul S. Jackson, Rockford, assignor to Rockford Machine Tool Company,Rockford, 111., a corporation of Illinois Application June 6, 1939,Serial No. 277,651

9 Claims.

This invention relates generally to machine tools having a supportactuated by a piston and cylinder device, such as planers, shapers,etc., and more particularly to a device'associated with the hydrauliccircuit of such piston and cylinder device for the purpose ofeliminating chatter of the support on its ways when operated at lowspeeds. to provide a new and improved mechanism for eliminating suchchatter.-

Although liquids are generally characterized as solid bodies andnon-compressible, it has been found in hydraulic circuits 'for machinetools that there is an appreciable compression of the oil, especiallywhen used in large volumes, as is required in the long cylinders oflarge metal planers. This compressibility is frequently due to air whichis entrained in the liquid, generally oil, either in a dissolved stateor a slightly foamy condition. The use of a lubricating oil as the fluidmedium in hydraulic circuits for machine tools is generally accepted,but the presence of air in the oil is a continuous source of annoyanceand prevents smooth operation of the reciprocating support that isdriven directly by the oil operating in a piston and cylinder device.The compressibility of the oil is evident, particularly on heavy loadsand at slow speeds, such as from Apparently, during such heavy cuts theair in the oil is compressed to a certain point before the resistance ofthe tool on the work is overcome, whereupon the table lunges forward andthe pressure of the oil drops, this cycle being repeated at a rela-'tively high rate on light machines, and at a relatively low rate onheavy machines. Although at It is the general object of the inventionment shown, it being contemplated that various and cylinder having oneend of the cylinder connected to said hydraulic circuit adjacent one endof the main cylinder and having in the other end of the auxiliarycylinder a coil spring or other resilient element for resisting movementof the auxiliary piston therein when subjected to the fluid pressure ofthe hydraulic circuit.

Other objects will become readily apparent from the following detaileddescription taken in connection with the accompanying drawing, in whichthe figure illustrates a preferred form of the invention associated withthe platen of a metal planer.

While I have illustrated in the drawing and shall hereinafter describein detail a detailed form of .the invention with a metal planer, it isto be understood that .I do not intend to limit the invention-to theparticular form and arrangechanges may be made by those skilled in theart without departing from the spirit and scope of the, appended claims.

As illustrated in'the drawing, numeral Ill represents platen or table ofa planer on which a Work piece II is secured in position to be cut by asuitable tool l2, the supporting means for which is not illustrated. Thetable is arranged to be reciprocated by means of a main piston andcylinder device having a cylinder l3 suitably supported on the bed ofthe machine (not shown) and a piston Hi. The piston I4 is secured to oneend of a piston rod l5, the other end of which extends out throughoneend of the cylinder and higher cutting speeds, such as those abovethirty feet per minute, this action of the table on its ways apparentlydoes not exist and the accompanying chatter is absent, the chatter atthe lower speeds and on heavy loads is extremely objectionable.

Another object is to provide a new and improved hydraulic circuit with acompensating device which is operable to eliminate such chatter of thedriven support. During the operation of the machine, this compensatorfunctions to maintain the pressure in the hydraulic circuit constant sothat a very smooth out of the tool is obtained.

Another object is to provide in a hydraulic circuit for a machine toolsupport having a main piston and cylinder actuating the support, ahydraulio circuit including said cylinder and a compensating devicecomprising an auxiliary piston is secured to a' depending portion l6 ofthe tabl III by means including a nut l1.

The invention contemplates the reciprocation of the table Ill by meansof a fluid, such as oil under pressure, the table generally being movedat a slow or feed rate toward the left during a cutting operation, andat a higher or traverse rate toward the right during the return stroke.The hydraulic circuit includes the main piston and cylinder device l3,l4, heretofore mentioned, a pumping mechanism l8 and valve mechanismdesignated generally IS. The pumping mechanism l8 and valve mechanism l9maybe of any one of a number of commercial products as, for example, atype D-R pump manufactured by The Oilgear Company of Milwaukee,Wisconsin. This pump consists generally of a tank or reservoir 20 onwhich the pump casing 2! is mounted,

the pump casing having amongst other mechanisms, a' gear type pump 22and a variable displacement piston type pump. Since the construction ofthe pumping mechanism It forms no part of the present invention, it willsuflice to say that 23 indicates a means for adjusting the speed of thetable during its cutting stroke toward the left, 2| indicates a meansfor adjusting the speed of the table during its return stroke toward theright, 25 indicates an automatic constant pressure relief valve in thereturn line to the tank 20, and 26 indicates a high pressure reliefvalve in a return line to the tank 20. The output of the gear pump 22 isconducted to the valve mechanism I! through a conduit 3!, whereas thehigh pressure fluid from the variable displacement piston pump of themechanism 13 is conducted to the valve mechanism by a conduit 3|. Theright hand end of the main cylinder I3 is connected to the valvemechanism I! by means of a conduit 33, and the left hand end or thecylinder I3 is connected to the valve mechanism is by means of a conduit33. A conduit 34 forms a return from the valve mechanism to the tank 20.and a conduit-35 forms a return from the valve mechanism to the pumpingmechanism It. A conduit 36 connects at one end to the valve mechanism l9and at the other end to the pumping mechanism I8, and functions tosupply fluid to internal parts of the pumping mechanism when it isdesired to obtain the maximum stroke of the variable stroke pumptherein. The operation of the valve mechanism is controlled by means ofa pilot having an operating member ID. This operating member isconnected to one 'end of a lever 4| pivoted at 42, the other end of thelever being connected by means of a rod 43 to one arm ll of a bellcrankdevice pivotally supported at 45. The other arm 43 of the bellcrankcarries a roller 41 positioned to be acted upon by a cam or dog 48secured to the table II or by a cam or dog 49 secured thereto, the dogsbeing effective at the ends of the cutting and return strokes,respectively, to cause reversal of the table by actuation of the pilotvalve.

More particularly, the invention in the form disclosed herein includesthe provision of a means or compensating device I for eliminatingchatter of the table on its ways when operating at relatively slowspeeds. This compensating device comprises an auxiliary cylinder ithaving an auxiliary piston i2 therein. The right hand end 4 of thecylinder is connected to the hydraulic circuit by means of a conduit 65which communicates with the conduit 33 adjacent the left hand end of themain cylinder I3. A risilient means in the form of a conically coiledspring 83 is positioned in the left hand end of the auxiliary cylinderSI to resist movement of the Dision 62 toward the left when subjected tothe pressure of the fluid in the hydraulic circuit. In order to providefor adjustment of the resistance exerted by the coiled spring 63, ascrew device it is threaded through the right hand end wall of thecylinder GI and carries a cupshaped member $1, between which and thepiston 62 a coiled spring 3 is positioned.

Under certain circumstances and in order to obtain an elimination ofchatter in both directions of operation of the table, a similarcompensating device 53 may be provided for the right hand end of themain cylinder l3. This compensating device comprises an auxiliarycylinder having an auxiliary piston 52 therein. The left hand end 53 ofthe cylinder is connected to the hydraulic circuit by means of a conduitwhich communicates with the conduit 33 adjacent the right hand end ofthe main cylinder l3. A resilient means in the form of a coiled springII is positioned in the ri ht hand end of the auxiliary cylinder ii toresist movement of the piston 52 toward the right when subjected to thepressure of the fluid in the hydraulic circuit. Preferably, a piston rod53 is connected to the piston 52 when it is desired to observe theaction of the piston 52 from a point externally of the cylinder. Inorder to avoid any build up of pressure in the right hand end of thecylinder 5| and the left hand end of cylinder 3| due to leakage of fluidpast the pistons therein, a return conduit II is provided for thecylinder ii and a return conduit Si is for the cylinder il. Theseconduits serve to drain the portions of the auxiliary cylinders to whichthey are connected.

In order to permit the use of one compensating device or the other, orboth, a suitable valve 65' is provided in the conduit ii and a valve 54'in the conduit 54 to permit of closing or opening said conduits. Inpractice, it is desirable that the conduits between the compensatingdevice cylinders and main cylinder l3 be as short as possible. In theevent only one com pensating device is used, it is preferable to use theone connected to that end of the main cylinder which is emptying duringthe cutting operation.

As mentioned hereinbefore, the preferred form of the invention isembodied in a hydraulic circuit for actuating the table of a metalplaner. Such machine tool generally has a mechanism for feeding the toolI! laterally of the work at the beginning of each stroke. This may beaccomplished by suitable means well known in the art, including a pistonand cylinder device ll.

In operating the circuit disclosed herein, fluid is first supplied tothe right hand end of the cylinder II for moving the table toward theleft through a cutting stroke during which the fluid from the left handend of the cylinder 3 passes back through the conduit 33 and valvemechanism It, thence through conduit 35 to the pumping mechanism II. Aportion of the fluid passing through conduit 3! continues downwardlyinto the tank 23 past the automatic constant pressure relief valve 25,whereas the remainder of this fluid passes to the intake of the pumpingmechanism so that only an amount of fluid equivalent to the volume ofthe piston rod I5 is caused to pass over the automatic constant pressurerelief valve 25. Upon completion of the cutting stroke, the dog 43engages the roller 41 so as to actuate the pilot valve member ll,whereupon the valve mechanism It is conditioned to direct fluid to theleft hand and of the cylinder l3 through conduit 33 for the purpose ofeffecting a return stroke of the table II. fluid from the right hand endof the cylinder l3 then passes out through the conduit 32 to the valvemechanism It. The valve mechanism is then adjusted so as to connect theadjacent ends of the conduits 32, 33 and 3|, so as to obtain a fastreturn stroke of the table through the differential action thusobtained. The table-continues in its return stroke toward the right\mtil the dog 43 thereon engages the roller 41 and pivots the bellcrankin a counterclockwise direction to effect a cutting stroke toward theleft. The table continues to reciprocate imtil the operator manipulatesa stop valve I! provided in the valve mechanism II.

In practice, it has been found that the mechanism herein disclosedeiiectively eliminates chatter. Furthermore, the compensating devicesoperate to cushion the reversals of the table, as

well as the movement or the table in the event "hard spots'areencountered in the work by the tool. The invention has been particularlyeffective in connection with heavy tables or heavily loaded tables whenoperated at slow speeds, such as twenty feet per minute or less inplaners.

Under such conditions, when heavy cuts are being taken, the oil in thehydraulic circuit or the air entrain therein compresses to a certainpoint where the resistance of the tool is overcome and then the tablelunges ahead, whereupon the pressure of the oil and any entrained airdrops, whereupon the table will momentarily stop until the necessarypressure is again built up. The rate at which this oscillation occurs isdependent to a considerable extent upon the weight oi the reciprocatingtable, oscillations and the attendant Q vibration of the table iseffectively eliminated by the invention disclosed herein. This isaccomplished by means of the compensator device because the pistonthereof will oscillate in the auxiliary cylinder so as to maintain thepressure in the hydraulic circuit substantially constant and maintain aregular fluid flow from the pumping mechanism to the main cylinder.

A second compensating device may be incorporated when it is desired toefiect smooth operation during the return stroke of the table, as wellas during the cutting stroke. When this compensating device is connectedin the circuit, it has been found desirable to close the automaticconstant pressure relief valve 25 entirely, with the result that anyreturn flow of oil in excess of that passing through the intake of thepumping mechanism returns to the tank 20 over the hydraulic pressurerelief valve 26.

I claim as my invention:

1. In a metal planer having a table, a main piston and cylinder devicefor actuating 'said table and a hydraulic circuit including pumpingmechanism and valve mechanism for supplying and controlling the flow offluid to and from the opposite ends of said cylinder, in combination, acompensating device comprising an auxiliary cylinder, a piston therein,a conduit connecting one end of said cylinder with said hydrauliccircuit adjacent one end of said main cylinder and a spring in the otherend of said auxiliary cylinder for resisting movement of the pistontherein.

2. In a metal planer having a table, a main piston and cylinder devicefor actuating said table and a hydraulic circuit including pumpingmechanism and valve mechanism for supplying and controlling the flow offluid to and from the opposite ends of said cylinder, in combination, acompensating device comprising an auxiliary cylinder, a piston therein,a conduit connecting one end of said cylinder with said hydrauliccircuit adjacent one end of said main cylinder and resilient means inthe other end of said auxiliary cylinder for resisting movement of thepiston therein.

3. In a metal planer having a table, a main piston and cylinder devicefor actuating said table and a hydraulic circuit including pumpingmechanism and valve mechanism for supplying and controlling the flow offluid to and from the opposite ends of said cylinder, in combination, acompensating device comprising an auxiliary cylinder, a piston therein,means connecting one end of said cylinder with said hydraulic circuit soas to subject the piston therein to the pressure of the fluid suppliedto said main cylinder and resilient means in the other end of saidauxiliary cylinder for resisting movement of the piston therein.

4. In a metal planer having a table, a mainpiston and cylinder devicefor actuating said table and a hydraulic circuit including pumpingmechanism and valve mechanism for supplying and controlling the flow offluid to and from the opposite ends of said main cylinder, incombination, a first compensating device comprising an auxiliarycylinder, a piston therein, means connecting one end of said cylinderwith said hydraulic circuit adjacent one end of said main cylinder,resilient means in the other end of said auxiliary cylinder forresisting movement of the piston therein, and a second compensatingdevice comprising a cylinder, a piston therein, resilient means in oneend of said last mentioned cylinder for resisting movement of the pistontherein, and means connectingthe other end of said cylinder to saidhydraulic circuit adjacent the other end of said main cylinder.

5. In a metal planer having a table, a main piston and cylinder devicefor actuating said table and a hydraulic circuit including pumpingmechanism and valve mechanism for supplying and controlling the flow offluid to and from the opposite ends of said cylinder, in combination, acompensating device comprising an auxiliary cylinder, a piston therein,a conduit connecting one end of said cylinder with said hydrauliccircuit adjacent the end of said main cylinder from which fluiddischarges during a cutting operation, and a spring in the other end ofsaid auxiliary cylinder for resisting movement of the piston therein.

6. In a metal planer having a table, a main piston and cylinder devicefor actuating said table and a hydraulic circuit including pumpingmechanism and valve mechanism for supplying and controlling the flow offluid to and from the opposite ends of said cylinder, in combination, acompensating device comprising an auxiliary cylinder, a piston therein,a conduit connecting one. end of said cylinder with said hydrauliccircuit adjacent one end of said main cylinder, and means for drainingfluid from the end of the auxiliary cylinder in which the resilientmeans is located.

'7. In a metal planer having a table, a main piston and cylinder devicefor actuating said table and a hydraulic circuit including. pumpingmechanism and valve mechanism for supplying and controlling the flow offluid to and from the opposite ends of said cylinder, in combination, acompensating device comprising an auxiliary cylinder, a piston therein,a conduit connecting one end of said cylinder with said hydrauliccircuit adjacent one end of said main cylinder, and means for adjusting.the tension of said spring.

8. In a metal planer having a table, a main piston and cylinder devicefor actuating said table and a hydraulic circuit including pumpingmechanism and valve mechanism for supplying and controlling the flow offluid to and from the opposite ends of said cylinder, in combination, acompensating device comprising an auxiliary cylinder, a piston therein,a conduit connecting the head end of said cylinder with said hydrauliccircuit adjacent one end of said main cylinder, a

draulic circuit adjacent one end of said main cylinder, resilient meansin the other end of said auxiliary cylinder for resisting movement ofthe piston therein, and a second compensating device comprising acylinder, a piston therein, resilient means in one end of said lastmentioned cylinder for resisting movement of the piston therein, and avalve device in each of the connecting means between the cylinders ofthe compensating de- 10 vices and the hydraulic circuit.

PAUL S. JACKSON.

